As in previous studies, the amphetamine-induced dopamine release was estimated by the reduction in dopamine D2 receptor availability measured with {123I]IBZM. The amphetamine-induced decrease in {123I}IBZM binding potential was significantly larger in the schizophrenic group compared to the control group. In the schizophrenic group, the elevated amphetamine effect on {123I]IBZM bindng potential was associated with emergence or worsening of positive psychotic symptoms. This result provide direct evidence that psychotic symptoms elicited by acute amphetamine in schizophrenic patients are associated with exaggerated stimulation of dopaminergic transmission and suggest an abnormal responsiveness of dopaminergic neurons in schizophrenia.